Gas-generating agent composition

ABSTRACT

There is provided a gas-generating agent composition having a very small pressure exponent and an extremely low pressure dependence of the burning rate. The gas-generating agent composition of the present invention contains a nitrogen-containing organic compound as a fuel and ammonium nitrate as an oxidizing agent, wherein the ratio of the nitrogen-containing organic compound to the ammonium nitrate (the former/the latter: weight ratio) is 35/65 or less. In the gas-generating agent composition, a copper compound may be further blended in a proportion of more than 0 part by weight and 30 parts by weight or less based on 100 parts by weight of the total amount of the nitrogen-containing organic compound and ammonium nitrate. The copper compound is preferably basic copper nitrate. Further, the nitrogen-containing organic compound is preferably a guanidine derivative, particularly preferably a guanidine nitrate.

TECHNICAL FIELD

The present invention relates to a gas-generating agent composition for an air bag inflator for motor vehicles and the like.

BACKGROUND ART

A non-azide gas-generating agent has been developed as a gas-generating agent composition for air bag systems mounted in vehicles such as motor vehicles, instead of sodium azide which has a problem in respect of toxicity. As the non-azide gas-generating agent, there has been proposed a gas-generating agent composition using a nitrogen-containing organic compound such as a guanidine derivative and a tetrazole as a fuel and ammonium nitrate as an oxidizing agent.

On the other hand, the air bag is required for the stability of development time particularly in terms of safety. The development time depends on the burning rate of a gas-generating agent. The burning rate generally tends to be affected by pressure, and the relationship between the burning rate and pressure is represented by the following expression (1):

r=aP^(n)  (1)

where r represents a burning rate; P represents a burning pressure; a represents a constant; and n represents a pressure exponent. a is a constant which varies with the type of a gas-generating agent composition and initial temperature. Thus, since the burning rate of a gas-generating agent is influenced by pressure, the development time will be unstable according to the circumstances of air bag development. However, when the pressure exponent n in the above expression (1) is small, the pressure dependence of the burning rate of the gas-generating agent will be reduced, allowing stable air bag development time to be obtained.

Japanese Patent Laid-Open No. 11-292678 discloses a gas-generating agent composition for air bags containing a guanidine derivative compound, a phase-stabilized ammonium nitrate and a silicon compound which acts as a pressure exponent controller or a detonation suppressing agent and having a pressure exponent n of 0.95 or less at a burning pressure P in the range of 50 to 70 kg/cm² determined from the above expression (1). However, as described in Examples, although the minimum value of n is 0.429, it is necessary to use a pressure exponent controller, and ammonium nitrate used needs to be phase-stabilized.

National Publication of International Patent Application No. 2002-522330 discloses a gas-generating composition containing ammonium nitrate, a highly oxygenated fuel such as guanidine nitrate and aminoguanidine nitrate, a phase stabilizer such as cesium nitrate, and a catalyst selected from copper and a copper compound. However, the minimum value of the pressure exponent shown in Examples is 0.56, and a phase stabilizer is required.

Japanese Patent No. 4248254 discloses a gas-generating agent composition containing a nitrogen-containing organic compound fuel and an oxidizing agent, wherein a part or all of the oxidizing agent is a heat-treated oxidizing agent obtained by mixing ammonium nitrate and basic copper nitrate and subjecting the mixture to heat-treatment at a temperature from 120° C. to 160° C. However, this literature does not at all describe the pressure exponent, and the oxidizing agent needs to be heat-treated.

Japanese Patent Laid-Open No. 2009-137819 discloses a gas-generating agent composition containing a fuel including ammonium nitrate and a binder, wherein a potassium salt of a water-soluble polymer which acts as a phase stabilizer of the ammonium nitrate is contained as the binder. However, this literature also does not at all describe the pressure exponent, and ammonium nitrate requires a phase stabilizer.

CITATION LIST Patent Literature Patent Literature 1: Japanese Patent Laid-Open No. 11-292678 Patent Literature 2: National Publication of International Patent Application No. 2002-522330 Patent Literature 3: Japanese Patent No. 4248254 Patent Literature 4: Japanese Patent Laid-Open No. 2009-137819 SUMMARY OF INVENTION Technical Problem

An object of the present invention is to provide a gas-generating agent composition having a very small pressure exponent and an extremely low pressure dependence of the burning rate.

Another object of the present invention is to provide a gas-generating agent composition which has the above characteristics and is easily prepared.

Solution to Problem

As a result of intensive studies for achieving the above objects, the present inventors have found that, for a gas-generating agent composition containing a nitrogen-containing organic compound as a fuel and ammonium nitrate as an oxidizing agent, when the ratio of the nitrogen-containing organic compound to ammonium nitrate is a specific value or less, it is possible to obtain a gas-generating agent composition having a significantly low pressure exponent without subjecting the raw material components to special treatment such as addition of a pressure exponent controller, and the present invention has been completed based on these findings.

Specifically, the present invention provides a gas-generating agent composition containing a nitrogen-containing organic compound as a fuel and ammonium nitrate as an oxidizing agent, wherein the ratio of the nitrogen-containing organic compound to ammonium nitrate (the former/the latter: weight ratio) is 35/65 or less.

In the gas-generating agent composition, ammonium nitrate may be one not subjected to phase-stabilizing treatment, and a pressure exponent controller may not be contained.

In the gas-generating agent composition, a copper compound may be further blended in a proportion of more than 0 part by weight and 30 parts by weight or less based on 100 parts by weight of the total amount of the nitrogen-containing organic compound and ammonium nitrate.

The copper compound is preferably basic copper nitrate. Further, the nitrogen-containing organic compound is preferably a guanidine derivative, particularly preferably guanidine nitrate.

Advantageous Effects of Invention

According to the present invention, since the ratio of the nitrogen-containing organic compound to ammonium nitrate is a specific value or less, the pressure exponent is very small as compared with a conventional one, and the pressure dependence of the burning rate is extremely low. Therefore, an air bag excellent in the stability of development time can be obtained.

DESCRIPTION OF EMBODIMENTS

The gas-generating agent composition of the present invention contains a nitrogen-containing organic compound as a fuel and ammonium nitrate as an oxidizing agent.

As the nitrogen-containing organic compound used as a fuel, a nitrogen-containing organic compound known as a fuel of a gas-generating agent such as a guanidine derivative, a tetrazole, a triazole, a hydrazine derivative, and a triazine derivative can be used. The nitrogen-containing organic compound can be used alone or in combination of two or more. Among the above nitrogen-containing organic compounds, a guanidine derivative is particularly preferred.

Examples of the guanidine derivative include guanidine nitrate, guanidine carbonate, guanidine perchlorate, nitroguanidine, aminonitroguanidine, aminoguanidine nitrate, aminoguanidine carbonate, aminoguanidine perchlorate, diaminoguanidine nitrate, diaminoguanidine carbonate, diaminoguanidine perchlorate, triaminoguanidine nitrate, and triaminoguanidine perchlorate. Among these, guanidine nitrate is particularly preferred.

The amount of the nitrogen-containing organic compound used is for example about 5 to 35% by weight, preferably about 7 to 33% by weight, more preferably about 8 to 30% by weight based on the whole gas-generating agent composition.

In the gas-generating agent composition of the present invention, ammonium nitrate is used as an oxidizing agent. Although ammonium nitrate is an oxidizing agent having good gas-generating efficiency, it has a large number of phase transition temperatures in the vicinity of room temperature, and as ammonium nitrate passes through these transition points, large volume changes take place, which tends to cause performance instability of the composition. Therefore, ammonium nitrate which is subjected to phase-stabilizing treatment is generally used to shift the phase transition points and to suppress the volume changes.

However, the gas-generating agent composition of the present invention has such a feature that a desired effect can be obtained without subjecting ammonium nitrate to phase-stabilizing treatment. However, a desired effect can also be obtained by subjecting ammonium nitrate to phase-stabilizing treatment.

When ammonium nitrate is subjected to phase-stabilizing treatment, a mixture containing ammonium nitrate and a phase stabilizer can be subjected to a suitable physical method, such as heating (at a temperature of, for example, 50° C. or more and less than 120° C., preferably 80° C. or more and 110° C. or less) an aqueous solution of ammonium nitrate, a phase stabilizer, and the like to evaporate and dry it to obtain a phase-stabilized ammonium nitrate.

Examples of the phase stabilizer include potassium salts such as potassium nitrate, potassium perchlorate, potassium chlorate, potassium chromate, potassium dichromate, potassium permanganate, potassium sulfate, potassium chloride, and potassium fluoride; and cesium salts such as cesium nitrate and cesium perchlorate.

The mixing ratio of ammonium nitrate to a phase stabilizer (for example, a phase stabilizer selected from potassium salts and cesium salts) can be arbitrarily set in the range where a residue during burning does not practically pose a problem, and it is generally in the range of an ammonium nitrate/phase stabilizer (weight ratio)=70/30 to 98/2, preferably an ammonium nitrate/phase stabilizer (weight ratio)=80/20 to 97/3. In the present invention, since a desired effect can be obtained without subjecting ammonium nitrate to phase-stabilizing treatment as described above, the ammonium nitrate/phase stabilizer (weight ratio) may be a value larger than 98/2 (for example, the ratio is 99/1 or more) even in the case where a phase stabilizer is used.

An anti-caking agent may be blended with ammonium nitrate. Examples of the anti-caking agent include magnesium oxide and powdered silica. The blending ratio of the anti-caking agent is about 0.05 to 2.0% by weight, preferably about 0.1 to 1.0% by weight based on the whole ammonium nitrate.

The amount of ammonium nitrate used is for example about 40 to 90% by weight, preferably about 45 to 85% by weight, more preferably about 50 to 75% by weight based on the whole gas-generating agent composition.

In the present invention, it is important that the ratio of the nitrogen-containing organic compound as a fuel to ammonium nitrate as an oxidizing agent (the former/the latter: weight ratio) is 35/65 or less. It is known that ammonium nitrate is an oxidizing agent which cannot stably burn because it has a high pressure exponent and the burning rate changes sensitively with pressure variation. When the ratio of the nitrogen-containing organic compound as a fuel to ammonium nitrate is set in the above range, the pressure exponent n can be surprisingly obtained as an extremely small value of 0.45 or less (for example, 0.3 to 0.45), and the pressure dependence of the burning rate (for example, a pressure range of 1 to 9 MPa) can be significantly reduced. Note that if the ratio of the nitrogen-containing organic compound to ammonium nitrate is larger than 35/65, the pressure exponent n will rapidly increase, for example, to a value of about 0.65 to 0.75, or more than these values.

The ratio of the nitrogen-containing organic compound to ammonium nitrate (the former/the latter: weight ratio) is preferably in the range of 30/70 or less. Although the lower limit of the ratio of the nitrogen-containing organic compound to ammonium nitrate (the former/the latter: weight ratio) is not particularly limited, it is practically about 20/80 in order to guarantee ignitability.

In the present invention, the ignitability will significantly be improved if a copper compound is further blended with the gas-generating agent composition as a burning promoter. Examples of the copper compound include basic copper nitrate, basic copper carbonate, copper oxide, copper hydroxide, copper sulfate, and copper nitrate. Among these, basic copper nitrate is particularly preferred. Note that, in the present invention, sufficient and stable burning property is obtained by only allowing ammonium nitrate and such a copper compound to coexist (even if they are heated, they are heated to less than 120° C., for example, 115° C. or less) without subjecting these components to heat-treatment at a temperature in the range of 120° C. to 160° C. as described in the above Japanese Patent No. 4248254.

The blending amount of the copper compound is for example more than 0 part by weight and 30 parts by weight or less, preferably 15 to 30 parts by weight, more preferably 15 to 25 parts by weight based on 100 parts by weight of the total amount the nitrogen-containing organic compound and ammonium nitrate.

The gas-generating agent composition of the present invention may further contain other additives as needed. Note that since the nitrogen-containing organic compound and ammonium nitrate are used at a specific proportion in the gas-generating agent composition of the present invention, an extremely small pressure exponent can be obtained without particularly containing a pressure exponent controller (for example, a silicon compound selected from silicon nitride, silicone, silicon carbide, silicon dioxide, silicates and clay minerals of silicates as described in Japanese Patent Laid-Open No. 11-292678). However, the gas-generating agent composition of the present invention may contain the above pressure exponent controller, and in this case, the content of the above pressure exponent controller in the gas-generating agent composition may be less than 0.3% by weight (for example, 0.2% by weight or less).

The gas-generating agent composition of the present invention can be formed into a desired shape. The forming method is not particularly limited, and, for example, press molding, tableting, extrusion, and the like can be employed. The shape of the formed gas-generating agent is not particularly limited, and examples include a pellet shape, a hollow cylindrical shape, and a porous columnar shape. The formed gas-generating agent may be a one-grain type. However, those having an extremely large change in the surface area during burning such as a spherical shape, a konpeitou-like shape, and a tetrapod shape are not preferred because they cause pressure fluctuation.

EXAMPLES

The present invention will be described in more detail below based on Examples, but the present invention is not limited by these Examples.

Examples 1 to 5, Comparative Examples 1 to 4

Guanidine nitrate (may be abbreviated as “GN”), ammonium nitrate (may be abbreviated as “AN”), and basic copper nitrate (may be abbreviated as “BCN”) were dry-blended to obtain gas-generating agent compositions each having the composition shown in Table 1. These compositions were press molded using a hydraulic cylinder under a pressure of 100 kg/cm² into a strand having a height of about 12.7 mm and a diameter of about 10 mm. Next, the surface of the strand was coated with an incombustible epoxy resin. The burning rate (mm/s) was measured in a nitrogen atmosphere of a specified pressure. The values of the pressure exponent n and the constant a were determined based on the following relational expression (1) between the burning rate (mm/s) and pressure (MPa):

r=aP^(n)  (1)

where r represents a burning rate; P represents a burning pressure; a represents a constant; and n represents a pressure exponent. Note that measurement of the burning rate was performed within the range of a burning pressure of 1 MPa to 9 MPa. The results are shown in Table 1.

TABLE 1 Gas-generating agent composition (parts by weight) Pressure (GN/AN/BCN) Constant a exponent n Example 1 20 80 20 1.00 0.44 Example 2 25 75 20 1.38 0.45 Example 3 30 70 15 1.99 0.34 Example 4 30 70 20 1.82 0.41 Example 5 35 65 20 2.74 0.41 Comparative 40 60 15 1.52 0.73 Example 1 Comparative 40 60 20 1.60 0.74 Example 2 Comparative 50 50 15 2.17 0.75 Example 3 Comparative 50 50 20 2.40 0.67 Example 4

As shown in Table 1, when the ratio of guanidine nitrate (GN) to ammonium nitrate (AN) (the former/the latter: weight ratio) is larger than 35/65, the pressure exponent n is about 0.65 to 0.75, but when the above ratio is 35/65 or less, the pressure exponent n rapidly decreased and showed an extremely small value of 0.3 to 0.45.

INDUSTRIAL APPLICABILITY

The gas-generating agent composition of the present invention or the gas-generating agent obtained by forming the composition can be used, for example, for an inflator for air bags of the driver's seat of a motor vehicle, an inflator for air bags of a seat next to the driver, an inflator for side air bags, an inflator for inflatable curtains, an inflator for knee bolsters, an inflator for inflatable seat belts, an inflator for tubular systems, a gas generator for pretensioners, and the like. 

1. A gas-generating agent composition containing a nitrogen-containing organic compound as a fuel and ammonium nitrate as an oxidizing agent, wherein the ratio of the nitrogen-containing organic compound to ammonium nitrate (the former/the latter: weight ratio) is 35/65 or less.
 2. The gas-generating agent composition according to claim 1, wherein ammonium nitrate is not subjected to phase-stabilizing treatment.
 3. The gas-generating agent composition according to claim 1 or 2, wherein a pressure exponent controller is not contained.
 4. The gas-generating agent composition according to claim 1, wherein a copper compound is further blended in a proportion of more than 0 part by weight and 30 parts by weight or less based on 100 parts by weight of the total amount of the nitrogen-containing organic compound and ammonium nitrate.
 5. The gas-generating agent composition according to claim 4, wherein the copper compound is basic copper nitrate.
 6. The gas-generating agent composition according to claim 1, wherein the nitrogen-containing organic compound is guanidine nitrate. 